The homopolymerization of cyclic vinyl ethers and copolymerization with certain classes of monomers is known to the art. One such cyclic vinyl ether is 3,4-dihydro-2H-pyran-2-methyl(3,4-dihydro-2H-pyran-2-carboxylate) which is commonly referred to as acrolein tetramer and has the structure: ##STR1##
The polymerization of this compound and its 2,5-dialkyl substituted derivatives is reported in U.S. Pat. No. 2,537,921 wherein the homopolymers are described as having excellent thermostability and resistance to water and solvents. Generally, however, such polymers tend to be brittle compositions. Among the many classes of comonomers which the patentee enumerates are unsaturated ethers and esters such as vinyl alkyl ethers, vinyl esters of carboxylic acids and other compounds containing polymerizable carbon-to-carbon double bonds none of which, however, are oxygen-heterocyclic compounds. Subsequent to the aforesaid patent, it was reported that divinyl ethers, and particularly the aforesaid di-(dihydropyranyl) compound (I) and bis-(dihydropyranyl) compounds, were capable of providing rigid, cellular polymeric products. Such products, which are referred to in the art as pyranyl-based foams, and their preparation, are reported in U.S. Pat. Nos. 3,311,574; 3,311,575; 3,318,824; and British Pat. No. 991,970. Notwithstanding the useful properties which pyranyl-based polymeric compositions possess, one property which detracts from and hinders their widespread commercial application is their poor friability resistance. In particular, Compound I which, from the standpoint of availability and relatively low cost, is the most attractive of the dipyranyl monomers, provides brittle and highly friable homopolymers and foamed polymeric products, although some improvement in friability is obtained by polymerization thereof in the presence of a phenolic compound such as 2,2-bis(4-hydroxyphenyl)-propane (Bisphenol-A).
It is an object of this invention, therefore, to provide new and improved polymeric compositions derived from cyclic vinyl ethers and, in particular, polymeric compositions derived from compounds containing a dihydropyranyl ring nucleus.
Another object is to provide new compositions of matter which are copolymerizable with dihydropyranyl compounds to produce products of improved friability resistance.
A further object is to provide improved foam formulations comprising, and improved polymeric foams derived from, 3,4-dihydro-2H-pyran-2-methyl (3,4-dihydro-2H-pyran-2-carboxylate).
Various other objects and advantages of this invention will become apparent to those skilled in the art from the accompanying description and disclosure.
In accordance with the present invention, the above objects are generally accomplished by providing polymeric compositions which comprise the polymerization reaction products of a di-(dihydropyranyl) compound and an oxygen-heterocyclic compound comprising at least one cyclic nucleus containing two oxygen atoms and from 3 to 4 carbon atoms arranged to provide a cyclic nucleus represented herein by the symbol D which has the following structure: ##STR2## wherein c has a value of zero or one as in the cyclic acetals, 1,3-dioxolanes and 1,3-dioxanes, respectively. One class of cyclic acetals which are employed in this invention are compounds containing only one of the aforesaid 1,3-dioxolanyl or 1,3-dioxanyl rings (referred to herein as monofunctional compounds) and having a hydroxyl-substituted monovalent organic radical bonded thereto. A second class of cyclic acetals are the difunctional 1,3-dioxolanes and 1,3-dioxanes (that is, compounds having two 1,3-dioxolanyl or 1,3-dioxanyl rings) and in which the respective dioxolanyl and dioxanyl rings are linked through a bivalent hydrocarbon group or a hydroxyl-substituted bivalent organic radical. A third class of suitable cyclic monomers for use in the present invention are the reaction products obtained by reacting the aforesaid hydroxyl-containing mono- or di-functional cyclic acetals with a dicarboxylic acid or an organic polyisocyanate, the polyisocyanate derivatives constituting new compositions of matter. A fourth class of cyclic acetals for use in the present invention are compounds in which one carbon atom of the aforesaid cyclic nucleus (D) in common to either a second cyclic nucleus (D) or a cycloaliphatic hydrocarbon nucleus, thereby providing spiro compounds containing from one to two 1,3-dioxolanyl or 1,3-dioxanyl rings.
In accordance with one embodiment of the process of the present invention, the aforesaid di-(dihydropyranyl) and cyclic acetals are copolymerized in a reaction medium comprising a cationic polymerization catalyst to provide polymeric products which are useful thermoset resins. In accordance with another embodiment of the process described herein, the aforesaid compounds are copolymerized in the presence of a cationic polymerization catalyst under conditions such that polymeric foams are produced.